It is known to polymerize solutions comprising alkenyl aromatic monomers having a diene rubber dissolved therein to form polyblends having a matrix phase of polymers of said monomers having dispersed therein particles of said diene rubber grafted with said monomers.
Mass and mass/suspension processes have been used to prepare such polyblends. U.S. Pat. No. 3,903,202 is one such suitable process for the continuous mass polymerization of such polyblends and it is hereby incorporated by reference.
The morphology of the rubber particles dispersed in the polyblend is critical to the final properties of the polyblend. Generally, the larger the size of said rubber particles, the greater the toughness and the smaller the size, the higher the gloss. Hence, the size of the rubber particles must be controlled to insure the control of the properties of the polyblend. U.S. Pat. No. 3,903,202 discloses that agitation during the early phases of polymerization disperses the dissolved rubber as particles and that higher rates of agitation generally decreases the size of said particles with lower rates of agitation producing larger particles.
Beyond the rubber particle size morphology and its contribution to toughness, it has been found that the internal morphology of the particle is also important to the rubber efficiency in toughening rubber reinforced polyblends.
It has been found that the greater the amount of grafted and occluded polymer produced in the rubber particle the greater its effective volume fraction becomes per concentration of rubber, hence, the greater its toughening efficiency. The total rubber, including graft and occlusions, is commonly called the gel content or insoluble portion of the polyblend when dissolved in a solvent for the matrix polymer phase.
The prior art continuous mass polymerization processes have attempted to increase the gel phase of polyblends by running the first reaction zone at less than about 15% conversion to occlude more monomer in the rubber phase as it is dispersed in the first reaction zones as disclosed in U.S. Pat. No. 3,658,946. Such processes require a plurality of reaction zones, i.e., three to four, since the first stage reaction zone only converts about 2 to 10% of the monomers and additional stages are required to finish the polymerization with heat and temperature control. Capital and energy costs become prohibitive in today's technology. U.S. Pat. No. 3,660,535 discloses a continuous mass process for rubber monomer solutions wherein the solutions are moved through stratified or plug flow reaction zones starting at zero conversion and ending at essentially 99% conversion through a plurality of staged reactors.
This process differs from that of U.S. Pat. No. 3,658,946 in that it is plug flow gradual polymerization having a gradual inversion of the rubber phase as the solution is polymerized from 0 to about 15 to 20% conversion. The process of U.S. Pat. No. 3,658,946 operates with steady-state polymerization reactors wherein the monomer-rubber solution enters a first reactor operating at less than 16% conversion and precipitates and disperses the rubber phase instantaneously with large amounts of occluded monomer in the rubber particles and then feeds the solution to subsequent reactors each operating at steady state conversion in stepwise fashion.
The present process differs from U.S. Pat. No. 3,658,946 process in that the first reaction zone is operating at an efficient 20 to 45% conversion and the monomer-rubber-polymer stream enters and disperses as a rubber particle having monomer and polymer occluded in the particle. It has been discovered that this monomer solution can be fed to high conversion efficient first reaction zones because the polymer in the reaction will not partition occluded monomers or polymer from the particles because the polymer in the particles holds the monomer in the particles having as high an affinity for the monomer as the polymer already formed in the reaction zone. In addition the block copolymers have the ability to hold the monomers and polymer in the rubber phase having a polybutadiene end compatible with the rubber phase and a polystyrene end compatible with the monomer and polymers to hold them in the rubber phase particles.
The present invention then provides a continuous process for preparing polyblends having increased rubber efficiency without using a large number of staged reactors. Efficient polymerization is provided in only two efficient polymerization zones running at high conversions and poly rates yet providing the polyblend produced with high rubber gel fractions.
It is the objective of the present invention to provide a process that will produce a rubber phase in polyblends and have an increased rubber volume fraction as a gel wherein larger amounts of grafted and occluded polymers are present in amounts of 1 to 5 parts per part of rubber.
It is the objective of the present invention to provide a continuous process wherein rubber-polymer-monomer solutions are polymerized in steady-state, flow-through, polymerization zones such that volume fraction of the rubber phase is increased beyond the contribution of the rubber moiety charged.